A drawer drive device by which a drawer or the like in a refrigerator is automatically set in an open state is described in Japanese Patent Laid-Open No. 2003-185333. A drawer drive device described in the Patent Literature includes a motor as a drive source and a linearly moving member which is connected with a drawer. Rotation of the motor is transmitted to the linearly moving member through a reduction gear train and a rotation-linear motion conversion mechanism and thereby the drawer is moved from a close position to an open position as the linearly moving member is moved in one direction.
The drawer which is to be moved from a close position to an open position by driving of a motor may be forcibly prevented from its movement by a user. In this case, a large force applied to the drawer by a user is transmitted to the motor through the rotation-linear motion conversion mechanism and the reduction gear train and thus structural members structuring the rotation-linear motion conversion mechanism and the reduction gear train and the motor may be damaged by the force. In order to prevent this damage, in the drive device in the above-mentioned Patent Literature, a torque limiter is arranged on the way of the reduction gear train so that a large force applied to the drawer is prevented from being transmitted to the motor.
The torque limiter described in above-mentioned Patent Literature is provided between two spur gears which are coaxially disposed. Further, one of two spur gears which are coaxially disposed is formed with a recessed part on an end face on the other spur gear side and the torque limiter is structured in the recessed part.
When a torque limiter is structured in the recessed part which is provided on an end face of a spur gear, a space for disposing the torque limiter is required to secure on its inner peripheral side and thus it is difficult to reduce the size of the spur gear in a radial direction.
If a space between a circumscribing circle which circumscribes the recessed part and a tooth tip circle of the spur gear is set to be small, the size of the spur gear can be reduced in the radial direction while securing a space structuring the torque limiter on an inner peripheral side of the spur gear. However, when the gear mechanism is structured as described above, a tube-shaped part which is located on an outer peripheral side relative to the recessed part of the spur gear may be easily damaged by a force which is transmitted through the torque limiter. Especially, in a case that the torque limiter is structured of inner teeth which are formed on a ring-shaped inner peripheral face of the recessed part and a torque limiter member provided with a locking pawl for engaging with the inner teeth, when a space between the circumscribing circle which circumscribes the recessed part and a tooth tip circle of outer teeth of the spur gear is set to be small, the thickness in the radial direction becomes extremely thin at a portion of the tube-shaped part where a tooth bottom of the outer teeth is located on its outer peripheral side and where a tooth bottom of the inner teeth is located on its inner peripheral side. Further, the thin portion is extended in an axial line direction and is formed at plural positions with a constant interval in the circumferential direction. As a result, strength of the spur gear is decreased and the spur gear is easily damaged.